Generally, a brake of a vehicle decelerates or stops the vehicle in operation, or maintains the vehicle at a standstill. When the brake operates, kinetic energy of the vehicle is converted into thermal energy by mechanical friction, and frictional heat is emitted therefrom to the atmosphere.
Vehicle brakes are divided into a drum-type hydraulic brake and a disc-type hydraulic brake. In a disc-type hydraulic brake, a braking force is generated when a disc is rotating together with a wheel instead of a drum, and the brake is strongly pressed by a frictional pad.
However, since hydraulic brakes require mechanical components, hydraulic pipes, and components for controlling a hydraulic pressure connected to a brake pedal of a driver's seat, their structure is complicated.
Accordingly, Electro-Mechanical Brakes (EMBs) have been recently used to simplify the structure of the braking apparatus.
Unlike typical hydraulic brakes, EMBs refer to brakes that obtain a braking force by pressing a frictional pad using a mechanism driven by an electric motor.
Common EMBs have an actuator including a motor that rotates for braking or braking release and applies pressure to the frictional pad using the torque of the motor to allow the disc to be pressurized or rubbed by friction. The EMBs receive a braking intention of a driver through the brake pedal, and then control a braking pressure of a wheel using the motor.
Since the EMBs, as the next-generation braking concepts, have quick response speed and enable precise control compared to the hydraulic brakes, the EMBs are expected to be preferentially applied to eco-friendly vehicles such as electric vehicles.
EMBs can also be achieved in combination with hydraulic brakes. For example, a hydraulic brake and an EMB can be applied to the front wheel and the rear wheel, respectively. Compared to a system adopting only a hydraulic brake, the combination system of the EMB and the hydraulic brake has a simple structure and an excellent braking force response with an easy control of the braking force.
Also, a Brake-By-Wire (BBW) system in which EMBs brakes are mounted in both front and rear wheels can be implemented. The BBW system performs braking by allowing electric calipers disposed at the front and rear wheels to hold the disc according to signals of a controller.
An Electro-Hydraulic Brake (EHB) system is another form of the BBW system and is different from the EMB. In the EHB system, a controller receives signals from a pedal travel sensor and a hydraulic sensor in a master cylinder to detect a driver's brake intention and requests deceleration and controls the hydraulic pressure of an accumulator through a solenoid valve to perform hydraulic braking on wheels.
Since the BBW system delivers a driver's braking intention using electric signals, there is no mechanical connection between the brake pedal and the wheel, and independent and precise control of the braking force on each wheel of a vehicle is possible. Furthermore, control of the braking force is easy, braking distance can be shortened, and braking stability can be increased.
The BBW system uses a pedal simulator to provide a hydraulic pedal-like feeling using hysteresis characteristics. The pedal simulator achieves the feeling of a pedal such as an existing hydraulic brake when a driver operates a pedal and assists the braking operation of a driver by forming a pedal repulsive force against the braking operation.
The BBW system is more advanced than typical braking apparatuses in which the characteristics of driver's pedal effort (force applied to the pedal) vs. braking force shows a single mode.
For example, when a driver steps on the brake pedal by force A1, the pedal variance (pedal depth, pedal travel, and pedal stroke) by force A1 is substantially equal to A2. When the pedal variance is A2, the braking force of the braking apparatus substantially shows a predetermined value A3 according to the pedal variance.
When the pedal operation variance is constant, the constant braking force is always generated to satisfy driver request deceleration. The pedal stroke according to a specific pedal effort, and the driver request deceleration and braking force corresponding to the pedal stroke are determined in a specific single mode. Also, variation patterns of the braking force according to pedal effort and the pedal operation variance are determined in a single mode.
Thus, in the related art, since the characteristics of the braking feeling of a vehicle according to pedal effort are not changed in a pre-designed single mode, and pedal effort or braking force characteristics cannot be changed according to driver's tendencies, sufficient braking force may not be achieved by, for example, women or elderly men.
Also, it is difficult to provide a sporty braking feeling to a driver who tends to enjoy sports driving.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.